I. Field of the Invention
The present invention relates to a method and apparatus for watermarking a digital image. The invention may be usefully employed in the newly emerging field of digital cinema.
II. Description of the Related Art
In the traditional film industry, theatre operators receive reels of celluloid film from a studio or through a distributor for eventual presentation in a theatre auditorium. The reels of film include the feature program (a full-length motion picture) and a plurality of previews and other promotional material, often referred to as trailers. This approach is well established and is based in technology going back around one hundred years.
Recently an evolution has started in the film industry, with the industry moving from celluloid film to digitized image and audio programs. Many advanced technologies are involved and together those technologies are becoming known as digital cinema. It is planned that digital cinema will provide a system for delivering full length motion pictures, trailers, advertisements and other audio/visual programs comprising images and sound at “cinema-quality” to theatres throughout the world using digital technology. Digital cinema will enable the motion picture cinema industry to convert gracefully from the century-old medium of 35 mm film into the digital/wireless communication era of today. This advanced technology will benefit all segments of the movie industry.
The intention is that digital cinema will deliver motion pictures that have been digitized, compressed and encrypted to theatres using either physical media distribution (such as DVD-ROMs) or electronic transmission methods, such as via satellite multicast methods. Authorized theatres will automatically receive the digitized programs and store them in hard disk storage while still encrypted and compressed. At each showing, the digitized information will be retrieved via a local area network from the hard disk storage, be decrypted, decompressed and then displayed using cinema-quality electronic projectors featuring high quality digital sound.
Digital cinema will encompass many advanced technologies, including digital compression, electronic security methods, network architectures and management, transmission technologies and cost-effective hardware, software and integrated circuit design. The technologies necessary for a cost-effective, reliable and secure system are being analyzed and developed. These technologies include new forms of image compression, because most standard compression technologies, such as MPEG-2, are optimized for television quality. Thus, artifacts and other distortions associated with that technology show up readily when the image is projected on a large screen. Whatever the image compression method adopted, it will affect the eventual quality of the projected image. Special compression systems have therefore been designed specifically for digital cinema applications to provide “cinema-quality” images at bit rates averaging less than 40 Mbps. Using this technology a 2-hour movie will require only about 40 GB of storage, making it suitable for transportation on such media as so-called digital versatile disks (DVDs) or transmission or broadcast via a wireless link.
While this has obvious advantages in terms of the distribution of movies, it brings with it its own problems in that in itself such transportation and transmission is not secure. Encryption and conditional access methods are therefore also being developed with the aim of preventing piracy of movies. In addition to digital theft, i.e., the theft of a pristine digital copy of the content of the DVDs and/or transmitted data, there is also the problem of optical theft. Optical theft is the recording of the image and audio content of a movie as it is being projected onto the screen of a theater. Optical theft is easy to perform using, for example, little more than a camcorder.